Dual Servo Valve Switching for Fail-Safe Propeller Pitch Control
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Solution Overview
Problem
Conventional propeller control valve systems are unreliable, often reverting to a null state that biases the actuator to one position if a valve fails, leading to uncontrolled propeller pitch.
Innovation Solution
A dual valve system with a main pump and auxiliary pump, low pressure line, return line, and a selection valve that can switch between primary and backup electro-hydraulic servo valves to maintain control, even in failure modes, with a cooling orifice to reduce leakage and extend auxiliary pump operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single valve system is used for propeller pitch control, then the system structure is simple, but the reliability deteriorates because the valve may fail and revert to a null state where pitch cannot be controlled
Solution Approach 1:
The single valve system is segmented into two separate valves (first valve and second valve), each capable of controlling pitch in opposite directions. This segmentation ensures that if one valve fails, the other can still maintain pitch control, thereby improving reliability without requiring a completely redundant dual-system architecture
Solution Approach 2:
The system incorporates a null state bias design where each valve is configured to bias the actuator toward a safe high-pitch position in the event of failure. This beforehand cushioning ensures that even when a valve fails, the system automatically defaults to a safe state, preventing complete loss of pitch control
2Duration of action of moving object
If an auxiliary pump with cooling orifice is added to extend operation during critical phases, then the duration of action is improved, but the device complexity increases
Solution Approach 1:
The cooling orifice is pre-installed in the auxiliary pump circuit to reduce hydraulic fluid leakage before critical phases occur. This preliminary action allows the auxiliary pump to operate longer by maintaining lower leakage rates, extending the duration of action without requiring additional complex cooling systems
Solution Approach 2:
The cooling orifice acts as an intermediary component that mediates between the auxiliary pump and the hydraulic fluid. By introducing this intermediate element, the system achieves extended pump operation through controlled leakage reduction without requiring direct complex thermal management systems
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The dual valve system enhances reliability and safety by allowing continued propeller pitch control with dual redundancy, reducing downtime and system complexity, and enabling extended operation on the auxiliary pump during critical phases.
Implementation Method 1
a cooling orifice can be connected between the pump line and the low pressure line
Implementation Method 2
the selection valve can be hydraulically actuated between the first selection position and the second selection position by being connected to the pump line on one side and selectively connected to the low pressure line via a solenoid and to the pump line via an orifice on another side
Implementation Method 3
a pressure actuator with a piston and at least a first port and a second port
Data Source
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AI summary
A system for controlling propeller pitch in the event of electro-hydraulic servo valve (EHSV) failure can include an actuator (101) and a selection valve (123) in fluid communication with the actuator. The selection valve can be fluid communication with a first EHSV (109) having a first null state bias configured to bias the actuator to an increased-pitch position, and a second EHSV (111) having a second null state bias configured to bias the actuator to a decreased-pitch position. The selection valve can be configured to selectively allow fluid communication between one of the first EHSV and actuator and/or the second EHSV and the actuator.